Stabilization of phenylphenols



United States Patent ice STABILIZATION OF PHENYLPHENOLS Harry Clough, Norton-on-Tees, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Application May 28, 1956 Serial No. 587,445

Claims priority, application Great Britain July 28, 1955 6 Claims. (Cl. 260--620) This invention relates to the stabilisation of phenol compounds containing relatively small quantities of alphanaphthol. v

In the production of phenolic substances, it is frequently observed that whereas immediately after preparation, the substances are light in colour, and possess a mild odour, they undergo more or less rapid deterioration on standing, developing a dark colour and unpleasant odour. This is a major disadvantage in many processes employing such phenolic substances, which in consequence frequently suffer considerable loss in value. The removal of the coloured and odoriferous substances is often laborious and expensive, and accordingly attempts have been made to prevent or limit their formation, rather than attempt to remove them once formed. It has been recognised that atmospheric oxidation often plays an important part, generally by the formation of coloured product from impurities present in the phenolic compounds.

We have found that the rate of formation of coloured product in this way in phenylated monohydroxy benzenes containing a relatively small quantity of alpha naphthol is greatly reduced by the presence of a small quantity of citric acid, tartaric acid or phosphoric acid.

According to the present invention, therefore, we provide a process for stabilising phenylated mono-hydroxy benzene containing less than approximately 3% by weight of alpha naphthol which comprises treating it with not more than approximately 5% by weight of citric acid, tartaric acid or phosphoric acid, or of any combination of these.

A very suitable method of treatment is by the use of an aqueous solution of the stabilising acid, but the process of the present invention may also be carried out by direct contact of the stabilising acid with the phenylated monohydroxy benzene; or the phenylated monohydroxy benzene may be precipitated from a solution in an organic solvent containing the phenylated monohydroxy benzene and the stabilising acid.

It is not necessary that the acid or acids with which the phenylated monohydroxy benzene is treated should be soluble therein; the stabilising effect remains if, after treatment with the stabilising acid or acids, the phenylated monohydroxy benzene is then subjected to processes such as Washing or recrystallisation, which might be expected to remove the stabilising acids which are present.

It is a preferred feature of the process of the present invention that the concentration limits of stabilising acid are 0.1 to 1% by weight of the phenylated hydroxy benzene and alpha naphthol to be treated.

The process of the present invention is particularly valuable in stabilising phenylated hydroxy benzene prepared by synthesis involving the hydrolysis of chlorbenzone. Appreciable quantities of alpha naphthol are formed and although much of this can be removed by other means, the small quantity which remains frequently gives rise to the formation of a coloured product on standing. The rate of formation of colour is greatly reduced by the addition of acids according to the process of the 5 alpha naphthol.

, 2,829,176 1 Patented Apr. 1, 1958 present invention, enhancing the value of the material by preserving its light colour.

The following example illustrates the effect of adding citric acid to ortho phenyl hydroxy benzene containing EXAMPLE Each test in this example was carried out on a molten sample in a one inch Lovibond cell, using a Lovibond Tintometer with red and yellow slides. The colours are expressed as where C =colour, and Y and R are respectively the yellow and red colour units required to match the sample. See Standard Methods for Testing Tar and its Products, 3rd edition, 1950, page 214, published by the Standardization of Tar Products Tests Committee, London.

When freshly distilled under vacuum, a sample of orthophenyl hydroxy benzene was found to contain approximately 1.5% by weight of alpha naphthol, and was almost colourless. Storage tests at room temperature and 100 C., and a colour test were carried out on the freshly distilled material. Other freshly distilled samples were treated according to the following tables:

Control: untreated ortho phenyl hydroxy benzene.

1st Test: molten ortho phenyl hydroxy benzene at 80 C. was contacted with 1.4% by weight of citric acid for minutes with occasional stirring; ortho phenyl hydroxy benzene was then decanted.

2nd Test: crushed ortho phenyl hydroxy benzene was stirred for 15 minutes with 1.4% of its weight of citric acid dissolved in sui'ficient water to give a 1% solution by weight. The solid product was then collected and sucked dry.

Table 2 Colour Values according to Y+3R Days at 100 G.

Control 1st; Test 2d Test Control: untreated ortho phenyl hydroxy benzene. 1st Test: molten ortho phenyl hydroxy benzene at 80 C. Was stirred for 30 minutes with 1.4% of its weight of citric acid dissolved in sufiicient water to give a 1% solution.

2nd Test: 40 grams ortho phenyl hydroxy benzene was dissolved in 20 mls. methanol, and 0.56 gram (i. e. 1.4%) citric acid dissolved in 25 mls. water were added. 35 mls. of methanol were added to restore homogeneity. 400 70 mls. water were then added, producing the product as an immiscible oil which crystallised on stirring, and which was collected and dried in vacuo at 40 C. for 1 hour.

Table 3 Colouraccording to C= Y-l-SR Days at Room See Table 1 for Test See Table 2 for Test Temp; Conditions 2 Conditions Control 151; 2d Control 1st 2d Test Test Test Test 1.6 1.6 1.6 0.8 0.8 0.8 l 8. l l 2. 1.7. 5 72 27. 5 48. 8 33. 2 18. 6 2.7. 9

I claim:

1. A process for stabilising phenylatedmonohydroxy benzene in the presence of up to 3% of alpha naphthol which comprises treating it with up to 5% of its weight of at least one acid selected from the group consisting of citric acid, tartaric acid and phosphoric acid.

2. A process according to claim 1 in which the said phenylated monohydroxy benzene is treated with 0.1 to 1% by weight of said acid;

3. A process according to claim 1 in which the said monohydroxy benzene is ortho phenyl phenol.

4. A composition of matter consisting essentially of a phenylated hydroxy benzene, and containing up to 3% by weight of alpha naphthol, and up to 5% by weight of at least one acid selected from the group consisting of citric acid, tartaric acid andphosphoric acid.

5. A composition of matter according to claim 4 in which said monohydroxy benzene is ortho phenyl phenol.

6. The composition of claim 5 containing no more than 3% by weight of said acid.

References Cited in the file of this patent UNITED STATES. PATENTS 2,672,485 Menn et a1 Mar. 16, 1954 

1. A PROCESS FOR STABILISING PHENYLATED MONOHYDROXY BENZENE IN THE PRESENCE OF UP TO 3% TO ALPHA NAPHTHOL WHICH COMPRISES TREATING IT WITH UP TO 5% OF ITS WEIGHT OF AT LEAST ONE ACID SELECTED FROM THE GROUP CONSISTING OF CITRIC ACID, TARTARIC ACID AND PHOSPHORIC ACID. 